'Healthy' Diets Don't Seem to Reduce MS Risk

by John Gever John Gever,Managing Editor, MedPage Today
September 15, 2014

Action Points

Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

BOSTON -- Dietary patterns in women did not appear to influence their risk of developing multiple sclerosis (MS), according to a large study with 2 decades of follow-up.

Among participants in the original Nurses' Health Study and the Nurses' Health Study II -- totaling more than 185,000 women -- rates of new-onset MS were similar irrespective of their rated adherence to four "heart-healthy" diets, said Dalia Rotstein, MD, of Brigham and Women's Hospital in Boston, and colleagues.

The only association reaching statistical significance was a reduced risk of MS diagnosis among participants whose self-reported food patterns throughout the follow-up period most resembled the Western diet normally associated with poor health outcomes (hazard ratio 0.66, P<0.05 versus low conformance to the Western diet), Rotstein said during a platform presentation at the European Committee for Treatment and Research in Multiple Sclerosis annual meeting, held jointly this year with its North American counterpart.

Participants with high adherence to a so-called prudent diet (high in vegetables, fruits, whole grains, and low-cholesterol animal proteins), the DASH diet, a Mediterranean-type diet, or a diet rated as healthy according to the Alternate Healthy Eating Index (also emphasizing fruits, vegetables, and low consumption of high-cholesterol foods) showed no lower rates of MS diagnosis than those with low adherence, with HRs of 0.89 to 1.15, all with P values much greater than 0.05.

Rotstein said the association between the Western diet -- high in red and processed meat consumption and low in unprocessed plant matter -- and reduced MS risk was probably a statistical fluke.

She also emphasized that the food intake data were all collected during participants' adulthood and said that dietary patterns during adolescence may be more influential on MS risk.

"Additional research is required to determine the possible role of diet quality in early years," she said.

Rotstein noted, too, that the study only addressed overall adherence to certain diet plans without examining intake of specific foods or nutrients, except for vitamin D supplementation. She acknowledged that specific diet components that genuinely influence MS risk might not have been captured in the current analysis.

Nevertheless, the study's broad implication is that overall diet "quality," according to standards now generally accepted for promotion of cardiovascular health, does not affect MS risk, Rotstein said.

She introduced her presentation by reviewing earlier studies of diet and MS, which mostly either found no association between dietary factors and disease risk or had conflicting results. These studies were limited by either a focus on individual components, such as polyunsaturated fatty acids or overall fat content, or by small participant samples.

The two Nurses' Health studies overcame these limitations in several ways, Rotstein said. They had enormous numbers of participants who were followed for 18 to 20 years, with food intake questionnaires administered at baseline and every 4 years. Data on a host of other potential risk factors were collected as well.

Overall, there were 480 cases of new-onset MS in the two studies, including 130 in the original cohort and 350 in the second.

These data allowed Rotstein and colleagues to rate participants' adherence to the five types of diet. The researchers calculated relative adherence scores and the statistical analysis was conducted on quintiles of these scores. The reported HRs were for the highest quintile (reflecting the greatest adherence to the specified diet) versus the lowest.

Adjustments were taken for age at enrollment, latitude of residence at age 15, body mass index at age 18, pack-years of smoking, overall caloric intake, race/ethnicity, and intake of supplemental vitamin D.

Rotstein reported HRs for adherence to the five diet types both from participants' baseline data and from the cumulative data during follow-up. Except for the association between high Western diet adherence throughout the study period and low MS risk, none of the HRs thus calculated reached statistical significance.

However, because there were relatively few MS cases diagnosed in the two cohorts, the 95% confidence intervals were relatively wide, approximately 30% to 40% in either direction.

Other limitations of the study included its restriction to mostly white professional women, the reliance on participants' self-reports of food intake and patterns, and the use of diet types mainly reflecting cardiovascular risk factors. Also, the current study is a secondary analysis of data collected for other purposes.

Rotstein said there could be "other more relevant patterns for immunological health."